Friction particles are compositions which find wide use in the formulation of friction elements. A friction element is a composition useful for imparting friction to a moving device without harming such device. Examples of friction elements are drum brake linings, disc brake pads, heavy-duty truck blocks and clutch plate facings. Generally about 5 to 15 weight percent of a friction element is composed of friction particles. A friction particle is a particulate material having the properties of no substantial softening, flowing together, or cohering at elevated temperatures. The friction particles are employed in the friction element for many reasons such as to reduce the frictional wear of the element, to smooth out the coefficient of friction values over wide temperature ranges and to provide a soft pedal action upon the application of the brake or similar device.
Friction particles have traditionally been prepared from cashew nutshell liquid (CNSL) which is a mixture of about 90 percent anacardic acid and 10 percent cardol. These friction particles have given very satisfactory results in friction element applications, but in recent years a number of disadvantages associated with their use have arisen. One major disadvantage is the rapidly increasing cost of the cashew oil. This is due to many facturs such as reduced and unreliable supply caused by bad weather conditions and political instability in the major exporting countries of the oil as well as the increasing costs associated with shipping the oil. Another problem is the highly dermatitic nature of the cardol component of the cashew oil; this is the cause of much disatisfaction among compounders of friction element formulations. A further disadvantage is the dusty nature of the friction particles due to the grinding process employed in their preparation; this dustiness is uncomfortable in itself and sometimes results in smoldering.
In response, there have been many efforts to synthesize a friction particle which will impart to a friction element the beneficial qualities of CNSL friction particles, but without the disadvantages of these friction particles. One such friction particle is disclosed in U.S. Pat. No. 3,864,304--this is a non-catalyzed product of the reaction at from about 225.degree. F. to 400.degree. F. of a non-hydroxy alkylated, hydroxy aromatic hydrocarbon-aldehyde resole containing substantially no etherified aromatic hydroxl groups with an alkylated hydroxy aromatic hydrocarbonaldehyde resole wherein the non-hydroxyalkylated resole comprises about 60 to 95 weight percent of the resin.
Because of the wide use of such friction particles in many devices commonly employed today, any new friction particle which can be synthetically produced and which will give comparable or improved performance over that obtained from conventional CNSL friction particles would be of great advantage.